In ultrasonic testing, a single element (conventional UT) or multiple elements such as phased array instruments are used to pulse on an object. The resulting echoes are received by the elements, digitized and analyzed to highlight any flaws in the targeted test object. Each element can be used to both send and receive high-frequency sound waves or echo signals, or they can be paired so that one element acts as a transmitter, the other one as a receiver.
Noises in echo signals are of normal presence in most types of ultrasonic testing. They are mixed in the echo signals but are not representative of the characteristics of the test objects. White noise can be from many sources such as thermally originated noise due to heat from electronics components. Existing efforts have been made to remove white noise.
In one existing effort, to help remove white noise, one could make many acquisitions then average out the response signals instead of pulsing only once. However, after every acquisition, the subsequent waveform inherits the previous waveforms' left-over energy, which is call “acoustic noise” in the processing channel. Therefore the challenge remains to remove or eliminate to the greatest degree both white noise and acoustic noise.
Averaging is made in another existing effort by means of digital processing for reducing white noise. All pulses are sent at a predetermine time step (Time “T”) with equal time intervals. Averaging is done for the multiple pulses fired. The resulting signals in the previous acquisition windows capturing each previous pulse are added to the subsequent acquisition windows. Unfortunately, for example, when the second pulse starts, there is still remaining acoustic energy called acoustic noise (or “tail”) left from the first pulse. The resulting signal inside the second acquisition window will then be corrupted by the “tail” of the first acquisition window. One skilled in the art can appreciated that the closer (in time) the pulses are to each other, the more acoustic noise will remain for the next pulse. This effect of acoustic noise resulted from conventional averaging will be further illustrated in the detailed description, in comparison to that to be minimized by using the solution herein disclosed.
U.S. Pat. No. 3,557,354 uses averaging to improve signal to noise ratio and reduce white noise. But it does not involve any effort in reducing acoustic noise caused by the accumulation process.
Another existing effort also found in U.S. Pat. No. 7,254,494 (later as '494) in which time shifting sequence of bursts (of ultrasound) is used to improve signal to noise ratio. However, '494 does not use averaging in its processing, instead deploys a method to identify the pattern of the sequence of burst, and then uses the information on the pattern for noise reduction.
It would be therefore adventurous to reduce white noise in ultrasonic testing devices by using averaging in digital data process, and address the drawbacks of previous effort by eliminating acoustic noise accumulated during the conventional averaging process.